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The mother of a Marine reservist who has spent the last four months in a Mexican jail spoke at a news conference Tuesday about what her son’s life is like in solitary confinement. NBC 7 military reporter Bridget Naso has details, including information defense’s strategy going forward. (Published Tuesday, Aug 5, 2014)

Updated at 7:36 PM CST on Tuesday, Aug 5, 2014

Attorneys for a U.S. Marine jailed in Mexico said Tuesday they will file a motion requesting a mistrial based on constitutional violations they claim occurred in the first eight hours their client was held by Mexican custom officials.

Sgt. Andrew Tahmooressi, of Weston, Florida, has been in Mexican custody facing weapons charges since he was arrested at the San Ysidro Port of Entry on April 1 with three U.S.-registered guns in his possession.

Jill Tahmooressi updated her son's condition Tuesday when she spoke to local media in Solana Beach, California.

For the first time, Tahmooressi's attorney Fernando Benitez explained why they are unable to get the charges dismissed for what they describe as an honest mistake by a misguided U.S. Marine.

“This is a case where a compounded series of mistakes has a young man in prison, fighting for his life,” Benitez said.

The Tahmooressi family was inexperienced in the Mexican legal system and missed the window of opportunity to file a motion to dismiss the charges, the attorney said.

Now, Benitez explains, they must go through the process and work for a positive outcome.

“We respect Mexican law and he was on Mexico soil with firearms and these are the consequences,” Jill Tahmooressi said.

On Monday, defense attorneys questioned Mexican officials about the eight hours Tahmooressi was detained after crossing the U.S.-Mexico border on April 1.

It was during this hearing that Benitez said he was able to gain the information needed for a motion to file for a mistrial.

He said the customs officials who stopped Tahmooressi testified Monday that a document designed to explain an individual's rights before a search was handed to the Marine after the search had begun. The document was also in Spanish.

Benitez said the paperwork necessary to perform the search of Andrew's vehicle was filled out days before the U.S. Marine crossed the border.

"Our contention is the search is illegal and everything resulting from that search is tainted with that same illegality and therefore cannot be used," Benitez said.

Benitez said that his client was not provided an interpreter or legal representation in the eight hours he was in the custody of customs officials, before he was presented to the Mexican federal prosecutor.

Benitez said that is not justified under the Mexican constitution.

Family members and friends have said Tahmooressi was confused and made a wrong turn into Mexico while carrying three U.S.-registered firearms in his truck.

Mexican officials claim they have information provided by U.S. authorities showing that Tahmooressi had entered through the same border crossing on three prior occasions.

The federal prosecutor Mario Galindo also released details about the specific firearms found in Tahmooressi's truck. Officials say they seized a 12-gauge loaded shotgun, a 5.56-caliber rifle loaded with a 30-round clip and with two additional clips, a .45-caliber loaded pistol, loaded with 10 .45-caliber rounds and with two additional clips.

Andrew Tahmooressi is being protected 24/7 while imprisoned and is able to call home twice a day, his mother said.

"There is a level of despondency I haven't seen before," she added.

When they speak, Jill said she reads the comments and prayers left on the family's Facebook page to her son to help lift his spirits.